1. Field of the Invention
The present invention relates to a display control apparatus and display control method, which display an image on a display area at a variable magnification ratio.
2. Description of the Related Art
In recent years, the performance of image sensing devices such as CCDs and CMOS sensors has been enhanced, and the number of pixels which can be used by them to sense an image has increased compared to conventional devices. A digital camera, which includes an image sensing device having a large number of pixels, can record image data having an image size, which cannot be entirely displayed on a display having a standard number of display pixels.
It has also become easy for end users to confirm whether or not a sensed image is visually in focus or whether or not an image adjustment result such as contrast adjustment or edge emphasis is desired by zooming out or in the sensed image to be displayed. For example, after the user senses an image using a digital camera provided with an image sensor having a large number of pixels, he or she displays the sensed image on a display of the digital camera. Then, the user zooms into the image displayed on the display by operating the digital camera, and checks if the image is visually in focus.
At this time, as is conventionally done, the user designates a desired part of the image displayed on the display to zoom into the image to have that part as the center. Japanese Patent No. 2557720 describes a technique which zooms into or out of an image with reference to the center of the image after changing the zoom-in ratio of the image.
According to the method of Japanese Patent No. 2557720, when an image is zoomed out with the center of a display range as a reference point, the position of the reference point is changed so as not to display an area outside the image, that is, outside a valid video area. For this reason, when the zoom-in and zoom-out processes of an image to be displayed within the display range are repeated, the display range is gradually moved to the center of the image, thus posing a problem.
This problem will be practically explained using FIGS. 17A to 17D. In FIGS. 17A to 17D, a part of an image 91 (to be referred to as a partial image hereinafter) is displayed on a display range 90. A case will be examined first wherein a partial image to be displayed in the display range 90 is to be zoomed out from a state exemplified in FIG. 17A. In this case, by increasing the display range 90 with respect to the image 91, the partial image displayed in the display range 90 is zoomed out.
The zoom-out processing of the partial image, that is, the increase processing of the display range 90 is executed with reference to a position 92 of the center of the display range 90 according to the related art. Then, as exemplified in FIG. 17B, a part of the display range 90 sticks out beyond the region of the image 91. Hence, by the method disclosed in Japanese Patent No. 2557720, the position of the display range 90 with respect to the image 91 is adjusted by a stick-out amount of the display range 90 from the image 91, so that the display range 90 falls within the region of the image 91, as exemplified in FIG. 17C.
Then, the zoomed-out partial image is zoomed in to a size before the zoom-out processing, that is, the display range 90 is decreased. When this processing is executed with reference to the position 92 of the center of the display range 90, the position of the display range 90 shifts with reference to the partial image before zoom-out processing (FIG. 17A) in the center direction of the image 91 by the position adjustment amount at the time of the zoom-out processing of the partial image. FIG. 17D shows this state.
In this way, when the position of the display range 90 with respect to the image 91 moves every time the zoom-in and zoom-out processes of the partial image are repeated, the user may feel that the displayed image is unnatural.